The Internet of Things is referred to as machine to machine (Machine to Machine, M2M) for short, and was first proposed in 1999. A definition is relatively simple: All objects are connected to the Internet by using information sensing devices, so as to implement smart identification and management. The objects are combined with the Internet, which can implement remote perception and control of all the objects; therefore, a smarter production and living system is generated. The Internet of Things is larger than the existing Internet, and is widely applied to multiple fields, such as a smart grid, intelligent transportation, environment protection, government work, public security, smart home furnishing, intelligent firefighting, industrial monitoring, elderly caring, and personal health.
The standardization organization 3rd generation partnership project (3GPP) dedicatedly founded a project team that studies enhancements and optimization that need to be made to a mobile communication network because of introduction of an machine type communication (MTC) device. Vodafone (Vodafone) proposes that, many M2M devices, such as an electric meter, may be placed at a location in which coverage is relatively poor, such as a basement, and these devices may need a coverage enhancement amount of 20 dB to meet a requirement. Even if user equipment sends a sequence always by using a maximum transmit power, a power received by a target base station still cannot reach a target receive power, and even is far lower than the target receive power. In this case, the user equipment may transmit a sequence at multiple transmission time intervals (TTI, Transmission Time interval), or transmit a sequence in multiple subframes (subframe), so as to achieve an effect of repeated sending. On a base station side, these sequences are collected and combined, so as to achieve an objective of improving a receive signal to noise ratio. For example:
Quantity of transmission time intervalsCoverage enhancement amount(#TTI)(dB)10 (reference for comparison)2345
There is a correspondence between a repetition count, that is, a quantity of occupied transmission time intervals, and information about a corresponding coverage enhancement amount (dB). This correspondence may be predefined after being obtained by means of mathematic calculation or in an emulation manner. Actual coverage statuses of user equipments differ greatly, not all users that need coverage enhancement need compensation as large as 20 dB, and an actual case is that the coverage enhancement amount may be an amount from 0 dB to 20 dB. In addition, quantities of transmission time intervals needed by user equipments that need different coverage enhancement amounts are different. User equipment that needs less coverage enhancement needs fewer transmission time intervals because needed coverage enhancement compensation may be obtained in a shorter accumulated time. Therefore, user equipments that need different coverage enhancements may be grouped, so that user equipments that need equal or close coverage enhancement amounts are clustered to form a group and use a same repetition count. In this way, a range that is from a coverage enhancement amount of 0 dB to a coverage enhancement amount of 20 dB may be divided into several groups, such as [5 dB, 10 dB, 15 dB, 20 dB]. Certainly, a system may also indiscriminately provide only one coverage enhancement amount, such as 15 dB or 20 dB.
In the prior art, to access a radio communications system, user equipment first performs a cell searching process to search for all possible cells and find an appropriate cell, and then performs a random access process to access a found target cell. After finding the appropriate cell and establishing downlink synchronization, the user equipment receives system information from a base station serving the target cell, where the system information includes a target receive power for transmitting a preamble sequence (preamble) in an uplink random access process to be performed by a UE.
When the base station receives at the same time signals sent by two user equipments from which distances to the base station are different, and because a signal of user equipment closer to the base station is relatively strong, and a signal of user equipment farther from the base station is relatively weak, the strong signal of the user equipment closer to the base station severely interferes with the signal of the other user equipment, that is, a near-far effect (near-far effect). A method for resolving this problem is: adjusting in real time transmit powers of the user equipments according to different communication distances, that is, power control is performed. When the user equipment initiates the uplink random access process to access the target base station, a transmit power of the preamble sequence is determined according to a target receive power of the preamble sequence and an uplink path loss (PL, path loss) between the user equipment and the target base station. The uplink PL may be obtained by estimating according to a downlink path loss that is between the target base station and the user equipment and is measured by the user equipment.
If a same coverage enhancement resource is provided in a system, users that need coverage enhancement all use a same quantity of coverage enhancement repetitions (a quantity of transmission time intervals). For example, a coverage enhancement of 15 dB is corresponding to 100 times of repeated transmissions (100 transmission time intervals). However, actual coverage enhancements needed by the user equipments are different. Because uplink path losses are different, some user equipments need only a relatively small coverage enhancement, for example, only 5 dB may meet a requirement of a target receive power; some user equipments need a relatively large coverage enhancement value so that the target receive power can be reached. If uplink path losses of user equipment 1 and user equipment 2 are different, an uplink path loss of the user equipment 1 is small and a coverage enhancement of 5 dB is needed, an uplink path loss of the user equipment 2 is large and a coverage enhancement of 15 dB is needed, and both the user equipment 1 and the user equipment 2 perform transmission by using a maximum transmit power, powers that are received at each transmission time interval by the target base station from the user equipment 1 and the user equipment 2 are also different, and the near-far effect appears at each transmission time interval. When the user equipment 1 and the user equipment 2 perform repeated transmission by using a same transmission time interval, accumulated total receive powers that are of the user equipment 1 and the user equipment 2 and are collected on a base station side are also different. If a total receive power accumulated after the user equipment 2 performs repeated transmission may exactly meet the requirement of the target receive power, a total receive power accumulated after the user equipment 1 performs repeated transmission is 10 dB (15 dB-5 dB) more than the target receive power. It can be learned that for the target base station, in addition to impact of normal receiving of the user equipment 2 due to the near-far effect, a receive power of the user equipment 1 is 10 dB higher than the target receive power, thereby greatly wasting a transmit power of the user equipment 1.